Bell, in U.S. Pat. No. 4,285,056, incorporated herein by reference, has disclosed an optical recording medium comprising a light reflective layer, a spacer layer and a light absorptive layer where the material of the spacer layer melts, sublimes or decomposes at a temperature at least 300.degree. C. or less than that of the material which comprises the light absorptive layer. Bell, in U.S. Pat. No. 4,300,227, incorporated herein by reference, has disclosed an improved version of this optical recording medium wherein the light absorptive layer melts at a temperature greater than 1000.degree. C. and the spacer layer is composed of an organic material. In each of these optical recording media information may be recorded as bubbles in the light absorptive layer. The bubbles produce an increase in the reflectivity of this recording medium on readout and have a high signal-to-noise ratio due to the absence of the irregular rim usually found about an opening in the light absorptive layer.
One problem with this approach to the recording of information is the limited range of powers of the recording beam over which the bubble can be formed without bursting. When the absorptive layer separates from the underlying spacer layer to form the bubble, the heat loss to the spacer layer and the substrate is reduced so that a small increase in recording power leads to a perforation or melt-through of the bubble in the light absorptive layer.
It would be desirable to have an optical recording medium in which information is recorded in the form of bubbles in the light absorptive layer, but for which the recording power range over which the bubbles are formed is increased.